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Abstract

Although the majority of coronary artery bypass graft (CABG) surgery patients are extubated within 6 to 8 hours following surgery, 20% to 40% of patients remain intubated 12 hours after surgery due to dysfunctional ventilator weaning response (DVWR). DVWR associated with increased morbidity and mortality (30% to 43%) following CABG surgery. Finding significant antecedence to predict DVWR could help to identify and prevent the complications from DVWR after CABG surgery. Literature review revealed that there is an association between cardiopulmonary indicators (CPI) and DVWR after CABG surgery. Cardiopulmonary indicators are the selected hemodynamic parameters that have an association with DVWR. The association of CPI with DVWR may be used to predict DVWR. Therefore, this study set out to find a predictive model for DVWR using CPI and significant antecedence.

The purposes of this research study were to describe the characteristics of CPI among patients with normal ventilator weaning response (NVWR) and dysfunctional ventilator weaning response (DVWR) after coronary artery bypass graft (CABG) surgery, to find the differences in characteristics of cardiopulmonary indicators between patients with NVWR and DVWR after CABG surgery, and to build a prediction model for DVWR with significant antecedence.

A retrospective case control study with time series design was utilized. An inclusion criteria guided purposive sampling technique was used to recruit 300 subjects from a retrospective audit of electronic medical records of patients who underwent CABG surgery between May 2003 and February 2006. Among the 300 subjects, 100 subjects constituted the case group and 200 constituted the control group. This study utilized descriptive and inferential statistical analysis, which was performed through SAS programs including PROC UNIVARIATE, PROC FREQ, PROC GLM, PROC REG, PROC MIXED REPEATED MEASURE ANOVA, and PROC LOGISTIC.

The study included such demographic variables as age and sex and clinical variables COPD, CHF, renal failure, number of grafts, and BSA, which were used for the description of the study sample as well as included in the analysis as covariates. The outcome variables of this study were DVWR and NVWR. The independent variable of the study was CPI, which included heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), cardiac output (CO), respiratory rate (RR), mixed venous oxygen saturation (SVO2), oxygen saturation (SPO2), pulmonary artery diastolic pressure (PAD) and pulmonary artery systolic pressure (PASP). An hourly time series measurement of selected CPI for 12 consecutive hours after CABG surgery was used to predict DVWR.

Findings revealed that several antecedence including COPD, CHF, MAP, RR, CO, PAD, and PASP were significantly associated with DVWR. In addition, findings revealed that the odds in favor of DVWR for patients with COPD were 5.466 times higher as compared to patients without COPD, holding all other variables constant. The odds in favor of DVWR for patients with CHF were 3.930 times higher than for patients without CHF, holding all other variables constant. The odds in favor of DVWR for patients with decrease 10mm/Hg mean MAP were 1.915 times the probability of NVWR, holding all other variables constant. This implies that hypotension increases risk of developing DVWR after CABG surgery. The odds in favor of DVWR for patients with decrease 5 points of mean RR were 2.978 times the probability of NVWR, holding all other variables constant. This implies that patients with lower RR are at risk of developing DVWR after CABG surgery. The odds in favor of DVWR for patients with decrease in mean CO by 2 points were 1.943 times the probability of NVWR, holding all other variables constant. This implies that patients with low CO are at the risk of developing DVWR after CABG surgery. The odds in favor of DVWR for patients with increase in mean PAD by 5mm/hg were 3.640 times the probability of NVWR, holding all other variables constant. This implies that patients with high PAD pressure are at risk of developing DVWR after CABG surgery. The odds in favor of DVWR for patients with decrease in mean PASP by 10mm/hg were 3.053 times the probability of NVWR, holding all other variables constant. This implies that the patients with low PASP are at risk of developing DVWR after CABG surgery.

In conclusion, the results of this study revealed significant antecedence to predict DVWR after CABG surgery, including COPD, CHF, MAP, RR, CO, PAD, and PASP. Therefore, this study concluded that the above-mentioned significant antecedence may be used to predict DVWR after CABG surgery in critical care. The implications from the conclusion are that the weaning protocols after CABG surgery may be tailored using these significant predictors. In addition, the study findings imply that patients with a history of COPD and CHF have significant risk of developing DVWR after CABG surgery. Therefore, this researcher recommends that weaning criteria be developed considering the above risk factors for high risk patients.